Bobbin



Feb- 19, 1957 N. P. HoFFsTEMDT l 2,781,985

BOBBIN Filed June 12, 1953 @l Z'gz /8 A! A//v/ v INVENToR:

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4United States Patent BOBBIN Nels P. Hotstedt, Chicago, Ill., assignerto William F. Stahl, Kenilworth, lll.

Application June 12, 1953, Serial No. 361,229

4 Claims. (Cl. 242-118) This invention relates to bobbins, and inparticular to bobbins of the type commonly used as a form for thewinding of transformers and electrical coils thereon.

Bobbins or coil forms are used extensively in the electrical industry assupports upon which coils of wire Vare wound to form transformers, chokecoils, etc. Conventionally, the bobbin construction includes a corehaving a ange mounted thereon adjacent each end. The flanges are usuallyprovided with `a central opening for receiving the core and are thensecured to the core by swaging the core ends to lock the flanges inplace. Where the core is square or rectangular or of some otherpolygonal or multiple sided construction resulting in corners that areoften sharp, the corresponding corners of the central opening of theflange do not snugly engage the core corners and are frequently out awayto allow swaging without deforming of the flanges. Another constructionis to provide the edges of the central opening with inwardlyextendingbulges to permit swaging Without distortion of the structure. In anyevent, the flanges have not satisfactorily enclosed the core, andopenings or irregular fits were provided, particularly at the cornerportions, or else inwardly-extending ribs provided a tight closure butwere difcult to form and resulted in an undesirable obstruction thatinterfered with the subsequent coil winding operation and furtherresulted in a coil having varying axial dimensions. The cutting out ofthe corners is not satisfactory since the coil vof wire subsequentlyWound upon the bobbin is not insulated by the flanges at the cornerportions nor otherwise protected by the flanges.

An object of the invention is to provide a bobbin having a core with aplurality of sides meeting in corners and in which terminal anges of thebobbin snugly engage the core throughout the entire periphery thereofand completely enclose the core. Another object is to provide a bobbinhaving a core that is polygonal in cross section with relatively sharpcorners and flanges equipped with laterally-extending projections snuglyreceiving the core; the flanges providing necks at the corners yof thecore and between adjacent projections whereby the flanges enclose thecore and provide a completely insulated space therebetween. Stillanother object is that of providing a bobbin structure as abovedescribed and in which the core is coated with a hard material providingswollen zones in the separations between adjacent projections at thecorners of the core to irmly anchor the anges upon the core. A lfurtherobject is in providing a bobbin or the like for electrical coils and inwhich the bobbin includes a multiple sided core with relatively sharpcorners having mounted thereon ilanges equipped with projections snuglyengaging the side `of the core; adjacent projections at the corner ofthe core being spaced and separated by necks struck laterally from theanges; a plastic coating on the core providing zones of enlargementwithin the spaces between the projections to lock the lianges upon thecore, whereby the more precise and accurately dimensioned bobbins areprovided at reduced cost While the flanges completely insulate windingsSubsequently ,sup-

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ported thereon. Additional objects and advantages will appear as thespecification proceeds.

An embodiment of my invention is illustrated in the accompanyingdrawing, in Which- Figure l is a side view in elevation of a bobbinconstructed according to my invention; Fig. 2 is an end view inelevation of the bobbin; Fig. 3 is a cross-sectional view taken on theline 3--3 of Fig. 1; Fig. 4 is a sectional view similar to that of Fig.3 but showing the parts in spacedapart relation prior to their assembly;and Fig. 5 is a sectional view taken on the line 5-5 of Fig. 2.

The structure of my invention consists of a bobbin. 10 having a core 11and terminal flanges 12 each equipped with a central aperture or opening13 therethrough. Adjacent the opening 13, each of the terminal anges 12is equipped with a plurality of laterally-extending or inwardly-struckVflanges or projections 14. As noted best in Fig. 2, the core 11 isrectangular in shape and this form is provided Vfor simplicity ofillustration and description. It is to be understood that the core 11 ispolygonal or multiple sided and adjacent sides meet at corners 15 thatare normally relatively sharp.

I prefer to provide an inwardly-extending projection 14 for each sidewall of the core 11, and between adjacent projections 14 that meet at acorner 15 of the core, separations or spacings therebetween areprovided. The separations or spacings are designated generally by thenumeral 16 and are seen best in Figs. l and 4. Between adjacentprojections 14 and in the spaces 16 at each corner of the core theflanges 12 are struck inwardly to provide necks 17. A neck 1'7 ispositioned at each corner 15 of the core and together with theprojections 14 completely enclose the core and provide a snug andregular t, as is seen best in Fig. 2.

The core 11 and the terminal anges 12 may be formed of any suitablematerial. In the usual construction the core 11 is formed of laminatedpaper, the laminations being secured together by adhesive or by othersuitable means. The terminal flanges 12 may also be paper that istreated or otherwise made relatively stiff. It will be understood thatthe central aperture or opening 13 through each of the terminal flanges12 will conform in size and shape to the contour of the core 11. It isalso preferred that the passage formed by the inwardly-extendingprojections 14 and necks 17 together with the opening 13 provide apassage that snugly receives the core 11 therein.

After the core 11 and flanges 12 have been formed, they are assembled asillustrtaed in Fig. 4 and the flanges are rigidly secured upon the core11 to provide a structure suitable for having electrical coils woundthereon and the anges completely enclose the core and thereby completelyinsulate and protect a coil or transformer subsequently wound upon thebobbin. I prefer to secure the llanges 12 to the core 11 in thefollowing manner. l coat the outer surface of the core 11 with a thinlayer of normally hard material 15 that may be, for example, celluloseacetate. The `core 11 with the outer hard layer of plastic or celluloseacetate thereon is snugly received within the central opening providedby each of the terminal flanges 12. The assembled bobbin is then placedin a chemical bath that is operative to soften the plastic layer 18.xposnre to the bath for an interval of from one to live seconds resultsin substantial swelling of the plastic layer which is in contact withthe bath. As a result the plastic layer promptly swells, as is indicatedin Fig. 5, and securely locks the flanges 12 in proper position upon thecore 1l.

Since spaces or separations are provided between adjacent projections 14at the corners 15 of the core, the plastic layer 18 will swell in theseseparations and abut and engage the projections 14 as well as the necks17.

l 3 These swollen zones will thereby lock or anchor the llanges 12 inrigid position upon the core 11.

The chemical bath for swelling the plastic layer 18 -may be any bathcontaining chemicals that will react with the particular plastic used tobring about a swelling thereof. If cellulose acetate is used for thecoating 18,

the bath may be methyl isobutyl ketone. 'Ihe method core 11 and thechemical baths that may be employed to bring about a swelling of; theplastic layer 18 is set out in detail in the application of William F.Stahl and AFred V. Collins, Serial No. 159,756, filed May 3, 1950, `nowPatent No. 2,644,651. Reference to this application may be made fordetails of both the method and bath composition.

The bobbin structure formed according to my invention is strong andstable and provides an excellent foundation upon which electrical coilsmay subsequently be wound. The projections 14 and necks 17 snuglyreceiv- ,ing the core 11 provide a completely enclosed core zone betweenflanges that insulates the coil wound therein and protects itmechanically throughout and particularly at the corners 15 of thepolygonal core.

While in the foregoing specification I have set forth a specificembodiment of my invention in considerable detail for purposes ofillustration, it is apparent that those skilled in the art may departfrom these details ywhile still falling within the spirit of theinvention.

yextending laterally therefrom in engagement with the coated sides ofsaid core, said projections being relatively long for engagement withthe sides of said core over extended areas thereof, said projectionsalong the adjacent edges thereof which lie along each corner of saidmultiple-sided core being recessed from the outer edges inwardly towardsaid flange to define open areas, said open areas terminating spaceddistances from said flange to provide restricted necks integral withsaid flange t that grip said core at the corners thereof, said coatingbeing swollen within the open areas defined by said projections andsubstantially abutting the projections and necks in the anchorage ofsaid flange upon said core.

2. A bobbin structure adapted for use as a coil form for the winding ofelectrical coils thereon, said bobbin structure comprising a polygonalcore having multiple sides meeting at corners extending longitudinallytherealong, said core having the outer surface thereof coated with anormally hard material adapted to swell and maintain itself in swollencondition upon the application of suitable swelling agents thereto, apair of flanges mounted thus employed for securing the flanges 12 uponthe :grumman upon said core, one adjacent each end thereof, each of saidflanges having a plurality of inwardly extending projections, one foreach side of said core, said projections lying along the coated sides ofsaid core in contiguous relation therewith and the projections of theflanges being in substantially abutting relation intermediate saidflanges, the adjacent projections of each flange being recessed at thecorners of said core to provide substantially continuous open areasextending from flange to flange along the corners of said core, and eachof said flanges being equipped with integral necks at the corners ofsaid core to define the terminal sides of said recesses and being ingripping relation with the corners of said core, said coating beingswollen to enlarged thickness in the open areas.

3. In a structure of the character described, a polygonal core, at leastone flange mounted upon said core, said flange being equipped with aplurality of projections extending laterally therefrom in substantialengagement with sides of said core along substantial areas thereof, saidprojections which lie along a corner of said core being recessed fromthe outer edges inwardly toward said flange to define an open area, saidopen area terminating a spaced distance from said flange to provide arestricted neck integral with said flange and gripping that corner ofsaid core, and a relatively hard material within the open area definedby such projections and in substantial abutment with the projections andsaid neck for anchoring said flange upon said core.

4. In combination, a multiple-sided member having corner portionsbetween at least certain of the sides thereof, a flange mounted uponsaid member and being equipped with a plurality of projections extendinglaterally therefrom in engagement with sides of said member, saidprojections bordering each of the corners of said member being recessedfrom the outer edges inwardly toward said flange to define open areas,each of said open areas terminating a spaced distance from said flangelto provide a restricted neck integral with said flange and ReferencesCited in the file of this patent UNITED STATES PATENTS 493,845 ScottMar. 2l, 1893 1,050,785 Austin et al. Jan. 21, 1913 1,953,035 Wyss Mar.27, 1934 2,299,113 Seever Oct. 20, 1942 2,644,651 Stahl et al. July 7,1953

